Techniques for clock recovery in a mobile information collection network following a power outage

ABSTRACT

Clock reference data may be recovered or updated in networks that include line-powered devices and other devices susceptible to power outages. For example, for a mobile information collection network, one or more devices with extended clock holdover may be strategically deployed throughout the mobile information collection network to provide reference clock data. As another example, battery-powered devices may be woken up in order to provide clock reference data to other devices. Alternatively or additionally, the battery-powered devices may be configured to periodically broadcast their clock reference data to other devices.

TECHNICAL BACKGROUND

The reading of electrical energy, water flow, and gas usage hashistorically been accomplished with human meter readers who came on-siteand manually documented meter readings. Over time, this manual meterreading methodology has been enhanced with walk by or drive by readingsystems that use radio communications to and from a mobile collectordevice in a vehicle. Recently, there has been a concerted effort toaccomplish meter reading using fixed communication networks that allowdata to flow from the meter to a host computer system without humanintervention.

Automated systems, such as Automatic Meter Reading (AMR) and AdvancedMetering Infrastructure (AMI) systems, may use radio frequency (RF)signals to collect data from transponders attached to meters thatmeasure usage of resources, such as gas, water and electricity. AMRsystems use a mobile data collector, such as a handheld computerequipped with RF technology or a vehicle-based RF system, to collectmeter data. In this document, terms such as “mobile interrogator”,“interrogator” and “mobile device” will be used to refer to a mobiledata collection platform. Such systems may employ a number of differentinfrastructures for collecting this meter data from the meters. Forexample, some automated systems obtain data from the meters using afixed wireless network that includes, for example, a central node, e.g.,a collection device, in communication with a number of endpoint nodes(e.g., meter reading devices (MRDs) connected to meters). At theendpoint nodes, the wireless communications circuitry may beincorporated into the meters themselves, such that each endpoint node inthe wireless network comprises a meter connected to an MRD that haswireless communication circuitry that enables the MRD to transmit themeter data of the meter to which it is connected. The wirelesscommunication circuitry may include a transponder that may or may not beuniquely identified by a transponder serial number. The endpoint nodesmay either transmit their meter data directly to the central node, orindirectly though one or more intermediate bi-directional nodes thatserve as repeaters for the meter data of the transmitting node.

Some networks may employ a mesh networking architecture. In suchnetworks, known as “mesh networks,” endpoint nodes are connected to oneanother through wireless communication links such that each endpointnode has a wireless communication path to a central node. This centralnode may be commonly referred to by several names including: gatekeeper;collector; and network access point. In this document, terms such as“gatekeeper” and “collector” will most often be used to refer to thisfunctionality. One characteristic of mesh networks is that the componentnodes can all connect to one another via one or more “hops.” Due to thischaracteristic, mesh networks can continue to operate even if a node ora connection breaks down. Accordingly, mesh networks areself-configuring and self-healing, significantly reducing installationand maintenance efforts.

Data collection systems such as electric, gas, and water utility systemstend to fall into two classifications: fixed or mobile network. Each hasadvantages and disadvantages. A fixed network typically has a treestructure with endpoints at the extreme ends of the tree. Theseendpoints relay their data toward a central head end by passing datafirst through a local area network (LAN) including other endpoints,repeaters, and collectors, and then through a wide area network (WAN) tothe head end. Data gathered by the head end may be analyzed, stored,presented and/or forwarded to other utility and consumer systems. Someunits, such as electricity meters, in a fixed network are always on.Other units, such as gas meters, water meters, and in-home modules, arebattery operated and may periodically receive a wake-up signal to tieinto the network. This periodic wake-up process can be unilateral at thediscretion of the endpoint or the result of a wake-up process initiatedby adjacent always-on devices.

A mobile network can be drive-by, fly-by, or walk-by in nature andtypically involves a mobile interrogator traveling a predetermined routeto gather data from endpoint devices in residential and commerciallocations. The mobile interrogator may also issue commands to theendpoint devices. The endpoint devices may include water, gas, andelectricity metering and control devices, such as thermostats and loadcontrol devices. There is typically little or no communication betweenendpoint devices themselves, and each endpoint device typicallymaintains its own history of data for the past collection period. Themobile interrogator wakes up the endpoint devices for the communicationexchange. Alternatively, the devices may unilaterally transmit theirdata periodically so that the mobile interrogator can receive the datawhenever it travels by. The collected data is passed from the mobileinterrogator to a route manager, and then up to a head end thatinterfaces to a utility billing system.

When power outages occur in an electric system, connected meters withautomated meter reading (AMR) functions may lose their reference clock.Even when local battery power is available, long duration outages canextend beyond the capability of the local battery power source tomaintain clock operations. Because modern meter automation systems use avariety of calendar and schedule-based events, this loss of referencetime can be critical.

SUMMARY OF THE DISCLOSURE

Clock reference data may be recovered or updated in networks thatinclude line-powered devices and other devices susceptible to poweroutages. For example, for a mobile information collection network, oneor more devices with extended clock holdover may be strategicallydeployed throughout the mobile information collection network to providereference clock data. As another example, battery-powered devices may bewoken up in order to provide clock reference data to other devices.Alternatively or additionally, the battery-powered devices may beconfigured to periodically broadcast their clock reference data to otherdevices.

One exemplary embodiment is directed to a system for efficientlyupdating clock reference data after a power outage in a mobileinformation collection network. The system may include one or moremobile mode communication nodes configured to communicate information toa mobile device when the mobile device moves within a physical proximityof the mobile mode communication nodes. The system may further includean extended clock holdover node configured to maintain the clockreference data after the power outage for a longer duration than themobile mode communication nodes. After power is restored at the mobilemode communication nodes, the extended clock holdover node may beconfigured to provide the clock reference data to the mobile modecommunication nodes.

Another exemplary embodiment is directed to a method for obtaining clockreference data from a battery powered device in a system comprising aplurality of mobile mode communication nodes configured to communicatedata to a mobile device when the mobile device moves within a physicalproximity of each of the mobile mode communication nodes. At least oneof the mobile mode communication nodes includes a battery-powereddevice. The method involves sending a wake-up signal and a clockreference request signal to the battery-powered device and receiving therequested clock reference data from the battery-powered device.

Yet another exemplary embodiment is directed to a system for obtainingclock reference data by a line-powered communication node for use in afixed wireless network comprising a plurality of communication nodes inwireless communication with a control node. Each communication node hasa wireless communication path to the control node that is either adirect path or an indirect path through one or more other communicationnodes that serve as repeaters. The system includes a line-poweredcommunication node and a battery-powered communication node thatperiodically transmits clock reference data as part of a fixed networkmessage. The line-powered communication node is configured to receivethe clock reference data transmitted by the battery-poweredcommunication node.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofvarious embodiments, is better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings exemplary embodiments of various aspectsof the invention; however, the invention is not limited to the specificmethods and instrumentalities disclosed. In the drawings:

FIG. 1 is a diagram of an exemplary metering system;

FIG. 2 expands upon the diagram of FIG. 1 and illustrates an exemplarymetering system in greater detail;

FIG. 3A is a block diagram illustrating an exemplary collector;

FIG. 3B is a block diagram illustrating an exemplary meter;

FIG. 4 is a diagram of an example subnet of a wireless network forcollecting data from remote devices;

FIG. 5A is a diagram of an exemplary prior art mobile informationcollection network;

FIG. 5B is a diagram of an exemplary mobile information collectionnetwork with an extended clock holdover device;

FIG. 6 is a process flow diagram illustrating an example method forobtaining clock reference data from a battery-powered device; and

FIG. 7 is a process flow diagram illustrating an example method forupdating clock reference data.

DETAILED DESCRIPTION

Exemplary systems and methods for gathering meter data are describedbelow with reference to FIGS. 1-7. It will be appreciated by those ofordinary skill in the art that the description given herein with respectto those figures is for exemplary purposes only and is not intended inany way to limit the scope of potential embodiments.

Generally, a plurality of meter devices, which operate to track usage ofa service or commodity such as, for example, electricity, water, andgas, are operable to wirelessly communicate. One or more devices,referred to herein as “collectors,” are provided that “collect” datatransmitted by the other meter devices so that it can be accessed byother computer systems. The collectors receive and compile metering datafrom a plurality of meter devices via wireless communications. A datacollection server may communicate with the collectors to retrieve thecompiled meter data.

FIG. 1 provides a diagram of one exemplary metering system 110. System110 comprises a plurality of meters 114, which are operable to sense andrecord consumption or usage of a service or commodity such as, forexample, electricity, water, or gas. Meters 114 may be located atcustomer premises such as, for example, a home or place of business.Meters 114 comprise circuitry for measuring the consumption of theservice or commodity being consumed at their respective locations andfor generating data reflecting the consumption, as well as other datarelated thereto. Meters 114 may also comprise circuitry for wirelesslytransmitting data generated by the meter to a remote location. Meters114 may further comprise circuitry for receiving data, commands orinstructions wirelessly as well. Meters that are operable to bothreceive and transmit data may be referred to as “bi-directional” or“two-way” meters, while meters that are only capable of transmittingdata may be referred to as “transmit-only” or “one-way” meters. Inbi-directional meters, the circuitry for transmitting and receiving maycomprise a transceiver. In an illustrative embodiment, meters 114 maybe, for example, electricity meters manufactured by Elster Solutions,LLC and marketed under the tradename REX.

System 110 further comprises collectors 116. In one embodiment,collectors 116 are also meters operable to detect and record usage of aservice or commodity such as, for example, electricity, water, or gas.In addition, collectors 116 are operable to send data to and receivedata from meters 114. Thus, like the meters 114, the collectors 116 maycomprise both circuitry for measuring the consumption of a service orcommodity and for generating data reflecting the consumption andcircuitry for transmitting and receiving data. In one embodiment,collector 116 and meters 114 communicate with and amongst one anotherusing any one of several wireless techniques such as, for example,frequency hopping spread spectrum (FHSS) and direct sequence spreadspectrum (DSSS).

A collector 116 and the meters 114 with which it communicates define asubnet/LAN 120 of system 110. As used herein, meters 114 and collectors116 may be referred to as “nodes” in the subnet 120. In each subnet/LAN120, each meter transmits data related to consumption of the commoditybeing metered at the meter's location. The collector 116 receives thedata transmitted by each meter 114, effectively “collecting” it, andthen periodically transmits the data from all of the meters in thesubnet/LAN 120 to a data collection server 206. The data collectionserver 206 stores the data for analysis and preparation of bills, forexample. The data collection server 206 may be a specially programmedgeneral purpose computing system and may communicate with collectors 116via a network 112. The network 112 may comprise any form of network,including a wireless network or a fixed-wire network, such as a localarea network (LAN), a wide area network, the Internet, an intranet, atelephone network, such as the public switched telephone network (PSTN),a Frequency Hopping Spread Spectrum (FHSS) radio network, a meshnetwork, a Wi-Fi (802.11) network, a Wi-Max (802.16) network, a landline (POTS) network, or any combination of the above.

Referring now to FIG. 2, further details of the metering system 110 areshown. Typically, the system will be operated by a utility company or acompany providing information technology services to a utility company.As shown, the system 110 comprises a network management server 202, anetwork management system (NMS) 204 and the data collection server 206that together manage one or more subnets/LANs 120 and their constituentnodes. The NMS 204 tracks changes in network state, such as new nodesregistering/unregistering with the system 110, node communication pathschanging, etc. This information is collected for each subnet/LAN 120 andis detected and forwarded to the network management server 202 and datacollection server 206.

Each of the meters 114 and collectors 116 is assigned an identifier (LANID) that uniquely identifies that meter or collector on its subnet/LAN120. In this embodiment, communication between nodes (i.e., thecollectors and meters) and the system 110 is accomplished using the LANID. However, it is preferable for operators of a utility to query andcommunicate with the nodes using their own identifiers. To this end, amarriage file 208 may be used to correlate a utility's identifier for anode (e.g., a utility serial number) with both a manufacturer serialnumber (i.e., a serial number assigned by the manufacturer of the meter)and the LAN ID for each node in the subnet/LAN 120. In this manner, theutility can refer to the meters and collectors by the utilitiesidentifier, while the system can employ the LAN ID for the purpose ofdesignating particular meters during system communications.

A device configuration database 210 stores configuration informationregarding the nodes. For example, in the metering system 200, the deviceconfiguration database may include data regarding time of use (TOU)switchpoints, etc. for the meters 114 and collectors 116 communicatingin the system 110. A data collection requirements database 212 containsinformation regarding the data to be collected on a per node basis. Forexample, a utility may specify that metering data such as load profile,demand, TOU, etc. is to be collected from particular meter(s) 114 a.Reports 214 containing information on the network configuration may beautomatically generated or in accordance with a utility request.

The network management system (NMS) 204 maintains a database describingthe current state of the global fixed network system (current networkstate 220) and a database describing the historical state of the system(historical network state 222). The current network state 220 containsdata regarding current meter-to-collector assignments, etc. for eachsubnet/LAN 120. The historical network state 222 is a database fromwhich the state of the network at a particular point in the past can bereconstructed. The NMS 204 is responsible for, amongst other things,providing reports 214 about the state of the network. The NMS 204 may beaccessed via an API 220 that is exposed to a user interface 216 and aCustomer Information System (CIS) 218. Other external interfaces mayalso be implemented. In addition, the data collection requirementsstored in the database 212 may be set via the user interface 216 or CIS218.

The data collection server 206 collects data from the nodes (e.g.,collectors 116) and stores the data in a database 224. The data includesmetering information, such as energy consumption and may be used forbilling purposes, etc. by a utility provider.

The network management server 202, network management system 204 anddata collection server 206 communicate with the nodes in each subnet/LAN120 via network 110.

FIG. 3A is a block diagram illustrating further details of oneembodiment of a collector 116. Although certain components aredesignated and discussed with reference to FIG. 3A, it should beappreciated that the invention is not limited to such components. Infact, various other components typically found in an electronic metermay be a part of collector 116, but have not been shown in FIG. 3A forthe purposes of clarity and brevity. Also, the invention may use othercomponents to accomplish the operation of collector 116. The componentsthat are shown and the functionality described for collector 116 areprovided as examples, and are not meant to be exclusive of othercomponents or other functionality.

As shown in FIG. 3A, collector 116 may comprise metering circuitry 304that performs measurement of consumption of a service or commodity and aprocessor 305 that controls the overall operation of the meteringfunctions of the collector 116. The collector 116 may further comprise adisplay 310 for displaying information such as measured quantities andmeter status and a memory 312 for storing data. The collector 116further comprises wireless LAN communications circuitry 306 forcommunicating wirelessly with the meters 114 in a subnet/LAN and anetwork interface 308 for communication over the network 112.

In one embodiment, the metering circuitry 304, processor 305, display310 and memory 312 are implemented using an A3 ALPHA meter availablefrom Elster Solutions, LLC. In that embodiment, the wireless LANcommunications circuitry 306 may be implemented by a LAN Option Board(e.g., a 900 MHz two-way radio) installed within the A3 ALPHA meter, andthe network interface 308 may be implemented by a WAN Option Board(e.g., a telephone modem) also installed within the A3 ALPHA meter. Inthis embodiment, the WAN Option Board 308 routes messages from network112 (via interface port 302) to either the meter processor 305 or theLAN Option Board 306. LAN Option Board 306 may use a transceiver (notshown), for example a 900 MHz radio, to communicate data to meters 114.Also, LAN Option Board 306 may have sufficient memory to store datareceived from meters 114. This data may include, but is not limited tothe following: current billing data (e.g., the present values stored anddisplayed by meters 114), previous billing period data, previous seasondata, and load profile data.

LAN Option Board 306 may be capable of synchronizing its time to a realtime clock (not shown) in A3 ALPHA meter, thereby synchronizing the LANreference time to the time in the meter. The processing necessary tocarry out the communication functionality and the collection and storageof metering data of the collector 116 may be handled by the processor305 and/or additional processors (not shown) in the LAN Option Board 306and the WAN Option Board 308.

The responsibility of a collector 116 is wide and varied. Generally,collector 116 is responsible for managing, processing and routing datacommunicated between the collector and network 112 and between thecollector and meters 114. Collector 116 may continually orintermittently read the current data from meters 114 and store the datain a database (not shown) in collector 116. Such current data mayinclude but is not limited to the total kWh usage, the Time-Of-Use (TOU)kWh usage, peak kW demand, and other energy consumption measurements andstatus information. Collector 116 also may read and store previousbilling and previous season data from meters 114 and store the data inthe database in collector 116. The database may be implemented as one ormore tables of data within the collector 116.

FIG. 3B is a block diagram of an exemplary embodiment of a meter 114that may operate in the system 110 of FIGS. 1 and 2. As shown, the meter114 comprises metering circuitry 304′ for measuring the amount of aservice or commodity that is consumed, a processor 305′ that controlsthe overall functions of the meter, a display 310′ for displaying meterdata and status information, and a memory 312′ for storing data andprogram instructions. The meter 114 further comprises wirelesscommunications circuitry 306′ for transmitting and receiving datato/from other meters 114 or a collector 116.

Referring again to FIG. 1, in the exemplary embodiment shown, acollector 116 directly communicates with only a subset of the pluralityof meters 114 in its particular subnet/LAN. Meters 114 with whichcollector 116 directly communicates may be referred to as “level one”meters 114 a. The level one meters 114 a are said to be one “hop” fromthe collector 116. Communications between collector 116 and meters 114other than level one meters 114 a are relayed through the level onemeters 114 a. Thus, the level one meters 114 a operate as repeaters forcommunications between collector 116 and meters 114 located further awayin subnet 120.

Each level one meter 114 a typically will only be in range to directlycommunicate with only a subset of the remaining meters 114 in the subnet120. The meters 114 with which the level one meters 114 a directlycommunicate may be referred to as level two meters 114 b. Level twometers 114 b are one “hop” from level one meters 114 a, and thereforetwo “hops” from collector 116. Level two meters 114 b operate asrepeaters for communications between the level one meters 114 a andmeters 114 located further away from collector 116 in the subnet 120.

While only three levels of meters are shown (collector 116, first level114 a, second level 114 b) in FIG. 1, a subnet 120 may comprise anynumber of levels of meters 114. For example, a subnet 120 may compriseone level of meters but might also comprise sixteen or more levels ofmeters 114. In an embodiment wherein a subnet comprises sixteen levelsof meters 114, as many as 2048 meters might be registered with a singlecollector 116.

As mentioned above, each meter 114 and collector 116 that is installedin the system 110 has a unique identifier (LAN ID) stored thereon thatuniquely identifies the device from all other devices in the system 110.Additionally, meters 114 operating in a subnet 120 comprise informationincluding the following: data identifying the collector with which themeter is registered; the level in the subnet at which the meter islocated; the repeater meter at the prior level with which the metercommunicates to send and receive data to/from the collector; anidentifier indicating whether the meter is a repeater for other nodes inthe subnet; and if the meter operates as a repeater, the identifier thatuniquely identifies the repeater within the particular subnet, and thenumber of meters for which it is a repeater. Collectors 116 have storedthereon all of this same data for all meters 114 that are registeredtherewith. Thus, collector 116 comprises data identifying all nodesregistered therewith as well as data identifying the registered path bywhich data is communicated from the collector to each node. Each meter114 therefore has a designated communications path to the collector thatis either a direct path (e.g., all level one nodes) or an indirect paththrough one or more intermediate nodes that serve as repeaters.

Information is transmitted in this embodiment in the form of packets.For most network tasks such as, for example, reading meter data,collector 116 communicates with meters 114 in the subnet 120 usingpoint-to-point transmissions. For example, a message or instruction fromcollector 116 is routed through the designated set of repeaters to thedesired meter 114. Similarly, a meter 114 communicates with collector116 through the same set of repeaters, but in reverse.

In some instances, however, collector 116 may need to quicklycommunicate information to all meters 114 located in its subnet 120.Accordingly, collector 116 may issue a broadcast message that is meantto reach all nodes in the subnet 120. The broadcast message may bereferred to as a “flood broadcast message.” A flood broadcast originatesat collector 116 and propagates through the entire subnet 120 one levelat a time. For example, collector 116 may transmit a flood broadcast toall first level meters 114 a. The first level meters 114 a that receivethe message pick a random time slot and retransmit the broadcast messageto second level meters 114 b. Any second level meter 114 b can acceptthe broadcast, thereby providing better coverage from the collector outto the end point meters. Similarly, the second level meters 114 b thatreceive the broadcast message pick a random time slot and communicatethe broadcast message to third level meters. This process continues outuntil the end nodes of the subnet. Thus, a broadcast message graduallypropagates outward from the collector to the nodes of the subnet 120.

The flood broadcast packet header contains information to prevent nodesfrom repeating the flood broadcast packet more than once per level. Forexample, within a flood broadcast message, a field might exist thatindicates to meters/nodes which receive the message, the level of thesubnet the message is located; only nodes at that particular level mayre-broadcast the message to the next level. If the collector broadcastsa flood message with a level of 1, only level 1 nodes may respond. Priorto re-broadcasting the flood message, the level 1 nodes increment thefield to 2 so that only level 2 nodes respond to the broadcast.Information within the flood broadcast packet header ensures that aflood broadcast will eventually die out.

Generally, a collector 116 issues a flood broadcast several times, e.g.five times, successively to increase the probability that all meters inthe subnet 120 receive the broadcast. A delay is introduced before eachnew broadcast to allow the previous broadcast packet time to propagatethrough all levels of the subnet.

Meters 114 may have a clock formed therein. However, meters 114 oftenundergo power interruptions that can interfere with the operation of anyclock therein. Accordingly, the clocks internal to meters 114 cannot berelied upon to provide an accurate time reading. Having the correct timeis necessary, however, when time of use metering is being employed.Indeed, in an embodiment, time of use schedule data may also becomprised in the same broadcast message as the time. Accordingly,collector 116 periodically flood broadcasts the real time to meters 114in subnet 120. Meters 114 use the time broadcasts to stay synchronizedwith the rest of the subnet 120. In an illustrative embodiment,collector 116 broadcasts the time every 15 minutes. The broadcasts maybe made near the middle of 15 minute clock boundaries that are used inperforming load profiling and time of use (TOU) schedules so as tominimize time changes near these boundaries. Maintaining timesynchronization is important to the proper operation of the subnet 120.Accordingly, lower priority tasks performed by collector 116 may bedelayed while the time broadcasts are performed.

In an illustrative embodiment, the flood broadcasts transmitting timedata may be repeated, for example, five times, so as to increase theprobability that all nodes receive the time. Furthermore, where time ofuse schedule data is communicated in the same transmission as the timingdata, the subsequent time transmissions allow a different piece of thetime of use schedule to be transmitted to the nodes.

Exception messages are used in subnet 120 to transmit unexpected eventsthat occur at meters 114 to collector 116. In an embodiment, the first 4seconds of every 32-second period are allocated as an exception windowfor meters 114 to transmit exception messages. Meters 114 transmit theirexception messages early enough in the exception window so the messagehas time to propagate to collector 116 before the end of the exceptionwindow. Collector 116 may process the exceptions after the 4-secondexception window. Generally, a collector 116 acknowledges exceptionmessages, and collector 116 waits until the end of the exception windowto send this acknowledgement.

In an illustrative embodiment, exception messages are configured as oneof three different types of exception messages: local exceptions, whichare handled directly by the collector 116 without intervention from datacollection server 206; an immediate exception, which is generallyrelayed to data collection server 206 under an expedited schedule; and adaily exception, which is communicated to the communication server 122on a regular schedule.

Exceptions are processed as follows. When an exception is received atcollector 116, the collector 116 identifies the type of exception thathas been received. If a local exception has been received, collector 116takes an action to remedy the problem. For example, when collector 116receives an exception requesting a “node scan request” such as discussedbelow, collector 116 transmits a command to initiate a scan procedure tothe meter 114 from which the exception was received.

If an immediate exception type has been received, collector 116 makes arecord of the exception. An immediate exception might identify, forexample, that there has been a power outage. Collector 116 may log thereceipt of the exception in one or more tables or files. In anillustrative example, a record of receipt of an immediate exception ismade in a table referred to as the “Immediate Exception Log Table.”Collector 116 then waits a set period of time before taking furtheraction with respect to the immediate exception. For example, collector116 may wait 64 seconds. This delay period allows the exception to becorrected before communicating the exception to the data collectionserver 206. For example, where a power outage was the cause of theimmediate exception, collector 116 may wait a set period of time toallow for receipt of a message indicating the power outage has beencorrected.

If the exception has not been corrected, collector 116 communicates theimmediate exception to data collection server 206. For example,collector 116 may initiate a dial-up connection with data collectionserver 206 and download the exception data. After reporting an immediateexception to data collection server 206, collector 116 may delayreporting any additional immediate exceptions for a period of time suchas ten minutes. This is to avoid reporting exceptions from other meters114 that relate to, or have the same cause as, the exception that wasjust reported.

If a daily exception was received, the exception is recorded in a fileor a database table. Generally, daily exceptions are occurrences in thesubnet 120 that need to be reported to data collection server 206, butare not so urgent that they need to be communicated immediately. Forexample, when collector 116 registers a new meter 114 in subnet 120,collector 116 records a daily exception identifying that theregistration has taken place. In an illustrative embodiment, theexception is recorded in a database table referred to as the “DailyException Log Table.” Collector 116 communicates the daily exceptions todata collection server 206. Generally, collector 116 communicates thedaily exceptions once every 24 hours.

In the present embodiment, a collector assigns designated communicationspaths to meters with bi-directional communication capability, and maychange the communication paths for previously registered meters ifconditions warrant. For example, when a collector 116 is initiallybrought into system 110, it needs to identify and register meters in itssubnet 120. A “node scan” refers to a process of communication between acollector 116 and meters 114 whereby the collector may identify andregister new nodes in a subnet 120 and allow previously registered nodesto switch paths. A collector 116 can implement a node scan on the entiresubnet, referred to as a “full node scan,” or a node scan can beperformed on specially identified nodes, referred to as a “partial nodescan.”

A full node scan may be performed, for example, when a collector isfirst installed. The collector 116 must identify and register nodes fromwhich it will collect usage data. The collector 116 initiates a nodescan by broadcasting a request, which may be referred to as a Node ScanProcedure request. Generally, the Node Scan Procedure request directsthat all unregistered meters 114 or nodes that receive the requestrespond to the collector 116. The request may comprise information suchas the unique address of the collector that initiated the procedure. Thesignal by which collector 116 transmits this request may have limitedstrength and therefore is detected only at meters 114 that are inproximity of collector 116. Meters 114 that receive the Node ScanProcedure request respond by transmitting their unique identifier aswell as other data.

For each meter from which the collector receives a response to the NodeScan Procedure request, the collector tries to qualify thecommunications path to that meter before registering the meter with thecollector. That is, before registering a meter, the collector 116attempts to determine whether data communications with the meter will besufficiently reliable. In one embodiment, the collector 116 determineswhether the communication path to a responding meter is sufficientlyreliable by comparing a Received Signal Strength Indication (RSSI) value(i.e., a measurement of the received radio signal strength) measuredwith respect to the received response from the meter to a selectedthreshold value. For example, the threshold value may be −80 dBm. RSSIvalues above this threshold would be deemed sufficiently reliable. Inanother embodiment, qualification is performed by transmitting apredetermined number of additional packets to the meter, such as tenpackets, and counting the number of acknowledgements received back fromthe meter. If the number of acknowledgments received is greater than orequal to a selected threshold (e.g., 8 out of 10), then the path isconsidered to be reliable. In other embodiments, a combination of thetwo qualification techniques may be employed.

If the qualification threshold is not met, the collector 116 may add anentry for the meter to a “Straggler Table.” The entry includes themeter's LAN ID, its qualification score (e.g., 5 out of 10; or its RSSIvalue), its level (in this case level one) and the unique ID of itsparent (in this case the collector's ID).

If the qualification threshold is met or exceeded, the collector 116registers the node. Registering a meter 114 comprises updating a list ofthe registered nodes at collector 116. For example, the list may beupdated to identify the meter's system-wide unique identifier and thecommunication path to the node. Collector 116 also records the meter'slevel in the subnet (i.e. whether the meter is a level one node, leveltwo node, etc.), whether the node operates as a repeater, and if so, thenumber of meters for which it operates as a repeater. The registrationprocess further comprises transmitting registration information to themeter 114. For example, collector 116 forwards to meter 114 anindication that it is registered, the unique identifier of the collectorwith which it is registered, the level the meter exists at in thesubnet, and the unique identifier of its parent meter that will serveras a repeater for messages the meter may send to the collector. In thecase of a level one node, the parent is the collector itself. The meterstores this data and begins to operate as part of the subnet byresponding to commands from its collector 116.

Qualification and registration continues for each meter that responds tothe collector's initial Node Scan Procedure request. The collector 116may rebroadcast the Node Scan Procedure additional times so as to insurethat all meters 114 that may receive the Node Scan Procedure have anopportunity for their response to be received and the meter qualified asa level one node at collector 116.

The node scan process then continues by performing a similar process asthat described above at each of the now registered level one nodes. Thisprocess results in the identification and registration of level twonodes. After the level two nodes are identified, a similar node scanprocess is performed at the level two nodes to identify level threenodes, and so on.

Specifically, to identify and register meters that will become level twometers, for each level one meter, in succession, the collector 116transmits a command to the level one meter, which may be referred to asan “Initiate Node Scan Procedure” command. This command instructs thelevel one meter to perform its own node scan process. The requestcomprises several data items that the receiving meter may use incompleting the node scan. For example, the request may comprise thenumber of timeslots available for responding nodes, the unique addressof the collector that initiated the request, and a measure of thereliability of the communications between the target node and thecollector. As described below, the measure of reliability may beemployed during a process for identifying more reliable paths forpreviously registered nodes.

The meter that receives the Initiate Node Scan Response request respondsby performing a node scan process similar to that described above. Morespecifically, the meter broadcasts a request to which all unregisterednodes may respond. The request comprises the number of timeslotsavailable for responding nodes (which is used to set the period for thenode to wait for responses), the unique address of the collector thatinitiated the node scan procedure, a measure of the reliability of thecommunications between the sending node and the collector (which may beused in the process of determining whether a meter's path may beswitched as described below), the level within the subnet of the nodesending the request, and an RSSI threshold (which may also be used inthe process of determining whether a registered meter's path may beswitched). The meter issuing the node scan request then waits for andreceives responses from unregistered nodes. For each response, the meterstores in memory the unique identifier of the responding meter. Thisinformation is then transmitted to the collector.

For each unregistered meter that responded to the node scan issued bythe level one meter, the collector attempts again to determine thereliability of the communication path to that meter. In one embodiment,the collector sends a “Qualify Nodes Procedure” command to the level onenode which instructs the level one node to transmit a predeterminednumber of additional packets to the potential level two node and torecord the number of acknowledgements received back from the potentiallevel two node. This qualification score (e.g., 8 out of 10) is thentransmitted back to the collector, which again compares the score to aqualification threshold. In other embodiments, other measures of thecommunications reliability may be provided, such as an RSSI value.

If the qualification threshold is not met, then the collector adds anentry for the node in the Straggler Table, as discussed above. However,if there already is an entry in the Straggler Table for the node, thecollector will update that entry only if the qualification score forthis node scan procedure is better than the recorded qualification scorefrom the prior node scan that resulted in an entry for the node.

If the qualification threshold is met or exceeded, the collector 116registers the node. Again, registering a meter 114 at level twocomprises updating a list of the registered nodes at collector 116. Forexample, the list may be updated to identify the meter's uniqueidentifier and the level of the meter in the subnet. Additionally, thecollector's 116 registration information is updated to reflect that themeter 114 from which the scan process was initiated is identified as arepeater (or parent) for the newly registered node. The registrationprocess further comprises transmitting information to the newlyregistered meter as well as the meter that will serve as a repeater forthe newly added node. For example, the node that issued the node scanresponse request is updated to identify that it operates as a repeaterand, if it was previously registered as a repeater, increments a dataitem identifying the number of nodes for which it serves as a repeater.Thereafter, collector 116 forwards to the newly registered meter anindication that it is registered, an identification of the collector 116with which it is registered, the level the meter exists at in thesubnet, and the unique identifier of the node that will serve as itsparent, or repeater, when it communicates with the collector 116.

The collector then performs the same qualification procedure for eachother potential level two node that responded to the level one node'snode scan request. Once that process is completed for the first levelone node, the collector initiates the same procedure at each other levelone node until the process of qualifying and registering level two nodeshas been completed at each level one node. Once the node scan procedurehas been performed by each level one node, resulting in a number oflevel two nodes being registered with the collector, the collector willthen send the Initiate Node Scan Response command to each level twonode, in turn. Each level two node will then perform the same node scanprocedure as performed by the level one nodes, potentially resulting inthe registration of a number of level three nodes. The process is thenperformed at each successive node, until a maximum number of levels isreached (e.g., seven levels) or no unregistered nodes are left in thesubnet.

It will be appreciated that in the present embodiment, during thequalification process for a given node at a given level, the collectorqualifies the last “hop” only. For example, if an unregistered noderesponds to a node scan request from a level four node, and therefore,becomes a potential level five node, the qualification score for thatnode is based on the reliability of communications between the levelfour node and the potential level five node (i.e., packets transmittedby the level four node versus acknowledgments received from thepotential level five node), not based on any measure of the reliabilityof the communications over the full path from the collector to thepotential level five node. In other embodiments, of course, thequalification score could be based on the full communication path.

At some point, each meter will have an established communication path tothe collector which will be either a direct path (i.e., level one nodes)or an indirect path through one or more intermediate nodes that serve asrepeaters. If during operation of the network, a meter registered inthis manner fails to perform adequately, it may be assigned a differentpath or possibly to a different collector as described below.

As previously mentioned, a full node scan may be performed when acollector 116 is first introduced to a network. At the conclusion of thefull node scan, a collector 116 will have registered a set of meters 114with which it communicates and reads metering data. Full node scansmight be periodically performed by an installed collector to identifynew meters 114 that have been brought on-line since the last node scanand to allow registered meters to switch to a different path.

In addition to the full node scan, collector 116 may also perform aprocess of scanning specific meters 114 in the subnet 120, which isreferred to as a “partial node scan.” For example, collector 116 mayissue a specific request to a meter 114 to perform a node scan outsideof a full node scan when on a previous attempt to scan the node, thecollector 116 was unable to confirm that the particular meter 114received the node scan request. Also, a collector 116 may request apartial node scan of a meter 114 when during the course of a full nodescan the collector 116 was unable to read the node scan data from themeter 114. Similarly, a node scan retry will be performed when anexception procedure requesting an immediate node scan is received from ameter 114.

The system 110 also automatically reconfigures to accommodate a newmeter 114 that may be added. More particularly, the system identifiesthat the new meter has begun operating and identifies a path to acollector 116 that will become responsible for collecting the meteringdata. Specifically, the new meter will broadcast an indication that itis unregistered. In one embodiment, this broadcast might be, forexample, embedded in, or relayed as part of a request for an update ofthe real time as described above. The broadcast will be received at oneof the registered meters 114 in proximity to the meter that isattempting to register. The registered meter 114 forwards the time tothe meter that is attempting to register. The registered node alsotransmits an exception request to its collector 116 requesting that thecollector 116 implement a node scan, which presumably will locate andregister the new meter. The collector 116 then transmits a request thatthe registered node perform a node scan. The registered node willperform the node scan, during which it requests that all unregisterednodes respond. Presumably, the newly added, unregistered meter willrespond to the node scan. When it does, the collector will then attemptto qualify and then register the new node in the same manner asdescribed above.

Once a communication path between the collector and a meter isestablished, the meter can begin transmitting its meter data to thecollector and the collector can transmit data and instructions to themeter. As mentioned above, data is transmitted in packets. “Outbound”packets are packets transmitted from the collector to a meter at a givenlevel. In one embodiment, outbound packets contain the following fields,but other fields may also be included:

Length—the length of the packet;

SrcAddr—source address—in this case, the ID of the collector;

DestAddr—the LAN ID of the meter to which the packet addressed;

RptPath—the communication path to the destination meter (i.e., the listof identifiers of each repeater in the path from the collector to thedestination node); and

Data—the payload of the packet.

The packet may also include integrity check information (e.g., CRC), apad to fill-out unused portions of the packet and other controlinformation. When the packet is transmitted from the collector, it willonly be forwarded on to the destination meter by those repeater meterswhose identifiers appear in the RptPath field. Other meters that mayreceive the packet, but that are not listed in the path identified inthe RptPath field will not repeat the packet.

“Inbound” packets are packets transmitted from a meter at a given levelto the collector. In one embodiment, inbound packets contain thefollowing fields, but other fields may also be included:

Length—the length of the packet;

SrcAddr—source address—the address of the meter that initiated thepacket;

DestAddr—the ID of the collector to which the packet is to betransmitted;

RptAddr—the ID of the parent node that serves as the next repeater forthe sending node;

Data—the payload of the packet;

Because each meter knows the identifier of its parent node (i.e., thenode in the next lower level that serves as a repeater for the presentnode), an inbound packet need only identify who is the next parent. Whena node receives an inbound packet, it checks to see if the RptAddrmatches its own identifier. If not, it discards the packet. If so, itknows that it is supposed to forward the packet on toward the collector.The node will then replace the RptAddr field with the identifier of itsown parent and will then transmit the packet so that its parent willreceive it. This process will continue through each repeater at eachsuccessive level until the packet reaches the collector.

For example, suppose a meter at level three initiates transmission of apacket destined for its collector. The level three node will insert inthe RptAddr field of the inbound packet the identifier of the level twonode that serves as a repeater for the level three node. The level threenode will then transmit the packet. Several level two nodes may receivethe packet, but only the level two node having an identifier thatmatches the identifier in the RptAddr field of the packet willacknowledge it. The other will discard it. When the level two node withthe matching identifier receives the packet, it will replace the RptAddrfield of the packet with the identifier of the level one packet thatserves as a repeater for that level two packet, and the level two packetwill then transmit the packet. This time, the level one node having theidentifier that matches the RptAddr field will receive the packet. Thelevel one node will insert the identifier of the collector in theRptAddr field and will transmit the packet. The collector will thenreceive the packet to complete the transmission.

A collector 116 periodically retrieves meter data from the meters thatare registered with it. For example, meter data may be retrieved from ameter every 4 hours. Where there is a problem with reading the meterdata on the regularly scheduled interval, the collector will try to readthe data again before the next regularly scheduled interval.Nevertheless, there may be instances wherein the collector 116 is unableto read metering data from a particular meter 114 for a prolonged periodof time. The meters 114 store an indication of when they are read bytheir collector 116 and keep track of the time since their data has lastbeen collected by the collector 116. If the length of time since thelast reading exceeds a defined threshold, such as for example, 18 hours,presumably a problem has arisen in the communication path between theparticular meter 114 and the collector 116. Accordingly, the meter 114changes its status to that of an unregistered meter and attempts tolocate a new path to a collector 116 via the process described above fora new node. Thus, the exemplary system is operable to reconfigure itselfto address inadequacies in the system.

In some instances, while a collector 116 may be able to retrieve datafrom a registered meter 114 occasionally, the level of success inreading the meter may be inadequate. For example, if a collector 116attempts to read meter data from a meter 114 every 4 hours but is ableto read the data, for example, only 70 percent of the time or less, itmay be desirable to find a more reliable path for reading the data fromthat particular meter. Where the frequency of reading data from a meter114 falls below a desired success level, the collector 116 transmits amessage to the meter 114 to respond to node scans going forward. Themeter 114 remains registered but will respond to node scans in the samemanner as an unregistered node as described above. In other embodiments,all registered meters may be permitted to respond to node scans, but ameter will only respond to a node scan if the path to the collectorthrough the meter that issued the node scan is shorter (i.e., less hops)than the meter's current path to the collector. A lesser number of hopsis assumed to provide a more reliable communication path than a longerpath. A node scan request always identifies the level of the node thattransmits the request, and using that information, an already registerednode that is permitted to respond to node scans can determine if apotential new path to the collector through the node that issued thenode scan is shorter than the node's current path to the collector.

If an already registered meter 114 responds to a node scan procedure,the collector 116 recognizes the response as originating from aregistered meter but that by re-registering the meter with the node thatissued the node scan, the collector may be able to switch the meter to anew, more reliable path. The collector 116 may verify that the RSSIvalue of the node scan response exceeds an established threshold. If itdoes not, the potential new path will be rejected. However, if the RSSIthreshold is met, the collector 116 will request that the node thatissued the node scan perform the qualification process described above(i.e., send a predetermined number of packets to the node and count thenumber of acknowledgements received). If the resulting qualificationscore satisfies a threshold, then the collector will register the nodewith the new path. The registration process comprises updating thecollector 116 and meter 114 with data identifying the new repeater (i.e.the node that issued the node scan) with which the updated node will nowcommunicate. Additionally, if the repeater has not previously performedthe operation of a repeater, the repeater would need to be updated toidentify that it is a repeater. Likewise, the repeater with which themeter previously communicated is updated to identify that it is nolonger a repeater for the particular meter 114. In other embodiments,the threshold determination with respect to the RSSI value may beomitted. In such embodiments, only the qualification of the last “hop”(i.e., sending a predetermined number of packets to the node andcounting the number of acknowledgements received) will be performed todetermine whether to accept or reject the new path.

In some instances, a more reliable communication path for a meter mayexist through a collector other than that with which the meter isregistered. A meter may automatically recognize the existence of themore reliable communication path, switch collectors, and notify theprevious collector that the change has taken place. The process ofswitching the registration of a meter from a first collector to a secondcollector begins when a registered meter 114 receives a node scanrequest from a collector 116 other than the one with which the meter ispresently registered. Typically, a registered meter 114 does not respondto node scan requests. However, if the request is likely to result in amore reliable transmission path, even a registered meter may respond.Accordingly, the meter determines if the new collector offers apotentially more reliable transmission path. For example, the meter 114may determine if the path to the potential new collector 116 comprisesfewer hops than the path to the collector with which the meter isregistered. If not, the path may not be more reliable and the meter 114will not respond to the node scan. The meter 114 might also determine ifthe RSSI of the node scan packet exceeds an RSSI threshold identified inthe node scan information. If so, the new collector may offer a morereliable transmission path for meter data. If not, the transmission pathmay not be acceptable and the meter may not respond. Additionally, ifthe reliability of communication between the potential new collector andthe repeater that would service the meter meets a threshold establishedwhen the repeater was registered with its existing collector, thecommunication path to the new collector may be more reliable. If thereliability does not exceed this threshold, however, the meter 114 doesnot respond to the node scan.

If it is determined that the path to the new collector may be betterthan the path to its existing collector, the meter 114 responds to thenode scan. Included in the response is information regarding any nodesfor which the particular meter may operate as a repeater. For example,the response might identify the number of nodes for which the meterserves as a repeater.

The collector 116 then determines if it has the capacity to service themeter and any meters for which it operates as a repeater. If not, thecollector 116 does not respond to the meter that is attempting to changecollectors. If, however, the collector 116 determines that it hascapacity to service the meter 114, the collector 116 stores registrationinformation about the meter 114. The collector 116 then transmits aregistration command to meter 114. The meter 114 updates itsregistration data to identify that it is now registered with the newcollector. The collector 116 then communicates instructions to the meter114 to initiate a node scan request. Nodes that are unregistered, orthat had previously used meter 114 as a repeater respond to the requestto identify themselves to collector 116. The collector registers thesenodes as is described above in connection with registering newmeters/nodes.

Under some circumstances it may be necessary to change a collector. Forexample, a collector may be malfunctioning and need to be takenoff-line. Accordingly, a new communication path must be provided forcollecting meter data from the meters serviced by the particularcollector. The process of replacing a collector is performed bybroadcasting a message to unregister, usually from a replacementcollector, to all of the meters that are registered with the collectorthat is being removed from service. In one embodiment, registered metersmay be programmed to only respond to commands from the collector withwhich they are registered. Accordingly, the command to unregister maycomprise the unique identifier of the collector that is being replaced.In response to the command to unregister, the meters begin to operate asunregistered meters and respond to node scan requests. To allow theunregistered command to propagate through the subnet, when a nodereceives the command it will not unregister immediately, but ratherremain registered for a defined period, which may be referred to as the“Time to Live.” During this time to live period, the nodes continue torespond to application layer and immediate retries allowing theunregistration command to propagate to all nodes in the subnet.Ultimately, the meters register with the replacement collector using theprocedure described above.

One of collector's 116 main responsibilities within subnet 120 is toretrieve metering data from meters 114. In one embodiment, collector 116has as a goal to obtain at least one successful read of the meteringdata per day from each node in its subnet. Collector 116 attempts toretrieve the data from all nodes in its subnet 120 at a configurableperiodicity. For example, collector 116 may be configured to attempt toretrieve metering data from meters 114 in its subnet 120 once every 4hours. In greater detail, in one embodiment, the data collection processbegins with the collector 116 identifying one of the meters 114 in itssubnet 120. For example, collector 116 may review a list of registerednodes and identify one for reading. The collector 116 then communicatesa command to the particular meter 114 that it forward its metering datato the collector 116. If the meter reading is successful and the data isreceived at collector 116, the collector 116 determines if there areother meters that have not been read during the present reading session.If so, processing continues. However, if all of the meters 114 in subnet120 have been read, the collector waits a defined length of time, suchas, for example, 4 hours, before attempting another read.

If during a read of a particular meter, the meter data is not receivedat collector 116, the collector 116 begins a retry procedure wherein itattempts to retry the data read from the particular meter. Collector 116continues to attempt to read the data from the node until either thedata is read or the next subnet reading takes place. In an embodiment,collector 116 attempts to read the data every 60 minutes. Thus, whereina subnet reading is taken every 4 hours, collector 116 may issue threeretries between subnet readings.

Meters 114 are often two-way meters—i.e. they are operable to bothreceive and transmit data. However, one-way meters that are operableonly to transmit and not receive data may also be deployed. FIG. 4 is ablock diagram illustrating a subnet 401 that includes a number ofone-way meters 451-456. As shown, meters 114 a-k are two-way devices. Inthis example, the two-way meters 114 a-k operate in the exemplary mannerdescribed above, such that each meter has a communication path to thecollector 116 that is either a direct path (e.g., meters 114 a and 114 bhave a direct path to the collector 116) or an indirect path through oneor more intermediate meters that serve as repeaters. For example, meter114 h has a path to the collector through, in sequence, intermediatemeters 114 d and 114 b. In this example embodiment, when a one-way meter(e.g., meter 451) broadcasts its usage data, the data may be received atone or more two-way meters that are in proximity to the one-way meter(e.g., two-way meters 114 f and 114 g). In one embodiment, the data fromthe one-way meter is stored in each two-way meter that receives it, andthe data is designated in those two-way meters as having been receivedfrom the one-way meter. At some point, the data from the one-way meteris communicated, by each two-way meter that received it, to thecollector 116. For example, when the collector reads the two-way meterdata, it recognizes the existence of meter data from the one-way meterand reads it as well. After the data from the one-way meter has beenread, it is removed from memory.

While the collection of data from one-way meters by the collector hasbeen described above in the context of a network of two-way meters 114that operate in the manner described in connection with the embodimentsdescribed above, it is understood that the present invention is notlimited to the particular form of network established and utilized bythe meters 114 to transmit data to the collector. Rather, the presentinvention may be used in the context of any network topology in which aplurality of two-way communication nodes are capable of transmittingdata and of having that data propagated through the network of nodes tothe collector. As a result, time-of-use and interval data collectionfunctionality can be restored more quickly. Recovering the clockreference data in this way may also facilitate determining the durationof the power outage.

According to the disclosure herein, clock reference data may berecovered or updated in networks that include line-powered devices andother devices susceptible to power outages. For example, for a mobileinformation collection network, one or more devices with extended clockholdover may be strategically deployed throughout the mobile informationcollection network to provide reference clock data. As another example,battery-powered devices may be woken up in order to provide clockreference data to other devices. Alternatively or additionally, thebattery-powered devices may be configured to periodically broadcasttheir clock reference data to other devices.

In greater detail, one of the techniques disclosed herein may involvestrategically deploying extended clock holdover devices throughout amobile information collection network in order to provide clockreference data. The extended clock holdover device may be, for example,a gatekeeper device, a collector device and/or a battery backed repeaterdevice. Such devices may often include a battery which may keep thedevice powered for an extended duration after a power outage hasoccurred.

As should be appreciated, devices such as gatekeepers are common infixed networks such as, for example, Advanced Metering Infrastructure(AMI) systems. In such fixed networks, the gatekeeper devices provide adata extraction point for downstream devices such as gas, water andelectricity meters. By contrast, mobile information collection networkssuch as, for example, Automatic Meter Reading (AMR) systems typically donot include devices such as gatekeepers. Instead, in mobile informationcollection networks, data is extracted by a mobile device that travelsto the physical proximity of the devices from which it extractsinformation.

FIG. 5A depicts an exemplary prior art mobile information collectionnetwork. As shown, the network 500 includes nodes 502, which may includedevices such as, for example, electricity meters. Information isextracted from the nodes 502 using a mobile device 506 that travelswithin a physical proximity of each node 502 in order to collectinformation from each node 502.

FIG. 5B depicts an exemplary mobile information collection network withan extended clock holdover device 510. As shown in FIG. 5B, anestablishment of communications between extended clock holdover device510 and nodes 502 may cause fixed communication paths 504 to beestablished between the extended clock holdover device 510 and at leastsome of the nodes 502. In the event of a power outage or another eventrequiring a clock update, the fixed paths 504 may allow clock referencedata to be provided by extended clock holdover device 510 to the nodes502. As should be appreciated, however, fixed paths 504 may often notserve as a mechanism for which information such as metering data iscollected from nodes 502. Rather, information such as metering data maycontinue to be collected from nodes 502 by the mobile device 506 just asin the prior art system of FIG. 5A.

In a mobile deployment without network or local gatekeepers or othernetwork devices with clock holdover, or after a prolonged power outageevent or in other scenarios, the internal clock of a battery-poweredendpoint device, such as a gas or water communication module, can beused to recover a reference clock. After restoration of power, meterpoints may not have a valid reference clock and may not be able torecover the clock from a local, e.g., RF-accessible, fixed network pointthat is always on, e.g., a line-powered device. Should this occur, thebattery-powered endpoint devices may often have a local clock that canbe provided to the always-on network points as a reference clock. Whilethis clock may not be the preferred reference, it can be used in theabsence of other clock sources until a higher precision clock sourcebecomes available. For a mobile network, a higher precision clock may bemade available by the actual mobile data collection device. However, themobile data collection device may not pass the meters that lost theclock reference for days or weeks. Having the ability to capture a localclock source shortly after power is restored, as opposed to having towait for a collection device to pass, allows the reestablishment of thereference clock for time-of-use and interval data collection purposes.It may also enable the calculation of the duration of the power outage.

When the battery-powered devices are operating in a fixed network, theytypically communicate to electricity meters only infrequently (forexample, every four hours) and send a message with metering data. Aftersending this message, the battery-powered devices may listen foradditional requests from devices that received the message. In a mobileenvironment, the battery-powered device may be configured toperiodically wake up (for example, every three seconds) and listen for awake-up message. If a wake-up message is received, the battery-powereddevice may then listen for a communication request, respond to therequest or requests if any have been received, and then return to alow-power sleep mode. Some battery-powered devices may operate in a“hybrid” mode in which the battery-powered devices are configured tosupport both fixed and mobile network communications. In such a hybridmode, the battery-powered device may listen for the wake-up message, butat a slower rate (for example, every ten seconds), and also periodicallysend the fixed network data message whether or not a wake-up message hasbeen received.

In one example embodiment, the battery-powered device operates in a modein which it is configured to work with a mobile network. In the mobilemode, the battery-powered device may listen for a wake-up toneperiodically (for example, every three seconds) and operate in alow-power sleep mode for the remainder of the time. In conventionalmobile information collection networks, the battery-powered devices aretypically woken up by the mobile data collection device in order toprovide information such as metering data to the mobile data collectiondevice. However, according to the present disclosure, thebattery-powered devices may also be woken up by other devices such aselectricity meters and other line-powered devices in order to provideclock reference data to such other devices.

Each electricity meter may be associated with one or morebattery-powered devices. Typically, a battery-powered device, such as agas or water metering device, is associated with the electricity meterthat serves the same residence. After a power failure occurs that causesthe electricity meter to lose its clock, the electricity meter may senda wake-up message to the gas or water metering device followed by a timerequest message. The response from the battery-powered device mayprovide the electricity meter with the clock reference data, e.g., dateand time.

Not all electricity meters need to be associated with a battery-powereddevice. In some networks, only a subset of electricity meters isassociated with battery-powered devices. Additionally, an electricitymeter need not necessarily be associated with a battery powered devicein order to request the clock reference data from that battery powereddevice. The electricity meters that receive time data from abattery-powered device may then be responsible for broadcasting orotherwise propagating the time data to other electricity meters in thenetwork. The electricity meter configuration may determine whether timeis requested from battery-powered devices and/or if time is thenbroadcast to other electricity meters.

FIG. 6 is a process flow diagram illustrating an example method 600 forobtaining clock reference data from a battery-powered device. At a step602, the line-powered device detects a power restoration subsequent to apower failure. As should be appreciated, events other than a powerfailure may also cause a need to obtain or update clock reference data.At a step 604, the line-powered device transmits a wake-up signal to thebattery-powered device. The line-powered device also sends a request fora clock reference to the battery-powered device at a step 606. At a step608, the line-powered device receives the clock reference data from thebattery-powered device. At a step 610, the line-powered device mayupdate its internal clock reference data in accordance with the clockreference data received from the battery-powered device. At a step 612,the line-powered device may broadcast the received clock reference datato other devices.

In some embodiments, the battery-powered device may be configured for afixed network mode of operation in which the battery-powered deviceperiodically broadcasts information such as metering data to “upstream”devices, which may include, for example, electricity meters. Theelectricity meters may then forward the information further upstream to,for example, gatekeepers and/or collectors. The techniques describedherein may allow clock reference data to be transmitted by thebattery-powered device as part of a fixed network information message toupstream devices. In this mode of operation, the battery-powered devicemay operate in a low-power sleep mode when not transmitting and may notbe configured to be woken via a wake-up message. The delay periodbetween transmissions of the fixed network messages including the clockreference data from the battery-powered devices may be variable.

In yet other embodiments, the battery-powered device may be configuredfor a “hybrid” mode of operation, in which the battery-powered deviceboth periodically listens for a wake-up message, as in the mobilenetwork mode of operation, and periodically broadcasts a fixed networkmessage regardless of whether a wake-up message has been received, as inthe fixed network mode of operation. In this scenario, thebattery-powered device may listen for a wake-up message less frequently(for example, every ten seconds) as compared with a battery-powereddevice 506 that is configured for strictly a mobile network mode ofoperation (for example, every three seconds). The battery-powered devicemay broadcast the fixed network message (for example, every four hours).Similarly to the mobile-only configuration, the electricity meter maytransmit a wake-up message after power is restored and the clock was notmaintained. Due to the less frequent wake-up interval from thebattery-powered device 506, the duration of the wake-up message from theelectricity meter may be longer than is involved for a battery-powereddevice that is configured for a mobile network mode of operation.

In addition to these configuration parameters, devices such aselectricity meters can have other configuration parameters set tocontrol the behavior relative to receiving clock reference data. Forexample, a “clock allowed” configuration parameter may define thedevices from which clock reference data may be accepted. A set of “clockpreference” configuration parameters may define the preferred clocksources and may define an order of priority of the preferred clocksources.

Devices such as electricity meters may also maintain not only the clock,but also the identity of the device from which clock reference data wasmost recently received. If valid clock reference data is received froman allowed source having a higher priority than the device from whichclock reference data was most recently received, the current meter clockmay be replaced with the clock from the source having the higherpriority.

FIG. 7 is a process flow diagram illustrating an exemplary method forupdating clock reference data. At a step 702, clock reference data isreceived from a first source. For example, an electricity meter mightreceive clock reference data from a battery-powered device such as a gasor water meter. At a step 704, internal clock reference data is updated.For example, the electricity meter might update its internal clock withthe reference data received from the battery-powered device. At a step706, the rank of the first source is stored. For example, theelectricity meter may maintain a record that its “current” clockreference data was obtained from the battery-powered device, which maybe a lower ranked device with lower precision data. The rankings may bebased on order of priority of clock reference data which may be storedby the electricity meter. At a step 708, clock reference data isreceived from a second source. For example, when the mobile deviceeventually moves within a physical proximity of the electricity meter,the mobile device may provide its clock reference data to theelectricity meter. At a step 710, it is determined whether the secondsource is ranked higher than the first source. If the second source isranked higher than the first source, then the clock reference data fromthe second source may be used to update the internal clock referencedata at a step 714. At a step 716, the rank of the second source isstored. For example, the electricity meter may determine that the mobiledevice is a higher ranked source than the battery-powered device and mayresponsively update its internal clock reference data with the data fromthe mobile device. The electricity meter may also maintain a record thatits “current” clock reference data has now been obtained from the mobiledevice. If, on the other hand, at step 710, it were determined that thesecond source was not ranked higher than the first source, then theclock reference data from the second source may be disregarded at a step712.

The types of devices that may provide clock reference data may include,but are not limited to, fixed network infrastructure devices, such asgatekeepers and/or collectors, repeaters, other electricity meters, orother line-powered devices; mobile data collection devices;battery-powered devices, such as gas and water communication devices;and home area network (HAN) devices. HAN devices may communicate via oneor more types of radios. For example, HAN devices may use the 900 MHzradio that is used for fixed network and mobile communications betweendevices and the fixed network or mobile network data collector. HANdevices may also communicate to electricity meters via different radiosuch as a 2.4 GHz radio. Multiple devices in the HAN may have validclocks, and HAN devices may be further prioritized to define thepreferred HAN device or devices.

In one example embodiment, the order of priority of sources for clockreference data may be as follows. Fixed network gatekeeper and/orcollector devices may have the highest priority. Fixed network repeaterdevices or other line-powered devices may have the next highestpriority. Mobile network collector devices may have the next highestpriority after line-powered devices. Battery-powered communicationmodules may have the next highest priority after mobile networkcollector devices. HAN devices may have the lowest priority, withnetwork-controlled HAN devices potentially having higher priority thannon-network-controlled HAN devices.

All or portions of the subject matter disclosed herein may be embodiedin hardware, software, or a combination of both. When embodied insoftware, the methods and apparatus of the subject matter disclosedherein, or certain aspects or portions thereof, may be embodied in theform of program code (e.g., computer executable instructions). Thisprogram code may be stored on a computer-readable medium, such as amagnetic, electrical, or optical storage medium, including withoutlimitation, a floppy diskette, CD-ROM, CD-RW, DVD-ROM, DVD-RAM, magnetictape, flash memory, hard disk drive, or any other machine-readablestorage medium, wherein, when the program code is loaded into andexecuted by a machine, such as a computer or server, the machine becomesan apparatus for practicing the invention. A device on which the programcode executes will generally include a processor, a storage mediumreadable by the processor (including volatile and non-volatile memoryand/or storage elements), at least one input device, and at least oneoutput device. The program code may be implemented in a high levelprocedural or object oriented programming language. Alternatively, theprogram code can be implemented in an assembly or machine language. Inany case, the language may be a compiled or interpreted language. Whenimplemented on a general-purpose processor, the program code may combinewith the processor to provide a unique apparatus that operatesanalogously to specific logic circuits.

While systems and methods have been described and illustrated withreference to specific embodiments, those skilled in the art willrecognize that modification and variations may be made without departingfrom the principles described above and set forth in the followingclaims. Accordingly, reference should be made to the following claims asdescribing the scope of the present invention.

What is claimed is:
 1. A system for efficient update of clock referencedata after a power outage in a mobile information collection network,the system comprising: one or more mobile mode communication nodesconfigured to communicate information to a mobile device when the mobiledevice moves within a physical proximity of the one or more mobile modecommunication nodes; and an extended clock holdover node configured tomaintain the clock reference data after the power outage for a longerduration than the one or more mobile mode communication nodes; wherein,after power is restored at the one or more mobile mode communicationnodes, the extended clock holdover node is configured to provide theclock reference data to the one or more mobile mode communication nodes,wherein the one or more mobile mode communication nodes each store anorder of priority of available sources from which to obtain the clockreference data, wherein the order of priority comprises the extendedclock holdover node, the mobile device, battery-powered devices and homearea network (HAN) devices, and wherein the one or more mobile modecommunication nodes are configured to replace clock reference datareceived from a lower priority source when different clock referencedata is subsequently received from a higher priority source.
 2. Thesystem of claim 1, wherein the extended clock holdover node comprises agatekeeper device, a collector device or a battery backed repeaterdevice, and wherein at least one of the one or more mobile modecommunication nodes comprises an electricity meter.
 3. A method forefficient update of clock reference data after a power outage in amobile information collection network comprising one or more mobile modecommunication nodes configured to communicate information to a mobiledevice when the mobile device moves within a physical proximity of theone or more mobile mode communication nodes, the method comprising:storing, in each of the one or more mobile mode communication nodes, anorder of priority of available sources from which to obtain the clockreference data, wherein the order of priority comprises an extendedclock holdover node, the mobile device, battery-powered devices and homearea network (HAN) devices, wherein the extended clock holdover node isconfigured to maintain the clock reference data after the power outagefor a longer duration than the one or more mobile mode communicationnodes; after power is restored at the one or more mobile modecommunication nodes: receiving, by the one or more mobile modecommunication nodes, clock reference data from a first source;receiving, by the one or more mobile mode communication nodes, clockreference data from a second source that is a higher priority sourcethan the first source; and replacing the clock reference data receivedfrom the first source with the clock reference data received from thesecond source.
 4. The method of claim 3, wherein the extended clockholdover node comprises a gatekeeper device, a collector device or abattery backed repeater device, and wherein at least one of the one ormore mobile mode communication nodes comprises an electricity meter. 5.A non-transitory computer readable storage medium having computerexecutable instructions stored thereon, the instructions, when executedby a processor, implementing a method for efficient update of clockreference data after a power outage in a mobile information collectionnetwork comprising one or more mobile mode communication nodesconfigured to communicate information to a mobile device when the mobiledevice moves within a physical proximity of the one or more mobile modecommunication nodes, the method comprising: storing, in each of the oneor more mobile mode communication nodes, an order of priority ofavailable sources from which to obtain the clock reference data, whereinthe order of priority comprises an extended clock holdover node, themobile device, battery-powered devices and home area network (HAN)devices, wherein the extended clock holdover node is configured tomaintain the clock reference data after the power outage for a longerduration than the one or more mobile mode communication nodes; afterpower is restored at the one or more mobile mode communication nodes:receiving, by the one or more mobile mode communication nodes, clockreference data from a first source; receiving, by the one or more mobilemode communication nodes, clock reference data from a second source thatis a higher priority source than the first source; and replacing theclock reference data received from the first source with the clockreference data received from the second source.
 6. The non-transitorycomputer readable storage medium of claim 5, wherein the extended clockholdover node comprises a gatekeeper device, a collector device or abattery backed repeater device, and wherein at least one of the one ormore mobile mode communication nodes comprises an electricity meter.